From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vlastimil Babka , Bob Liu , Sasha Levin , Wanpeng Li , Michel Lespinasse , KOSAKI Motohiro , Rik van Riel , David Rientjes , Mel Gorman , Hugh Dickins , Joonsoo Kim , Andrew Morton , Linus Torvalds Subject: [PATCH 3.14 137/158] mm: try_to_unmap_cluster() should lock_page() before mlocking Date: Sun, 4 May 2014 11:40:46 -0400 Message-Id: <20140504154048.636475765@linuxfoundation.org> In-Reply-To: <20140504154029.975081050@linuxfoundation.org> References: <20140504154029.975081050@linuxfoundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vlastimil Babka commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c upstream. A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin fuzzing with trinity. The call site try_to_unmap_cluster() does not lock the pages other than its check_page parameter (which is already locked). The BUG_ON in mlock_vma_page() is not documented and its purpose is somewhat unclear, but apparently it serializes against page migration, which could otherwise fail to transfer the PG_mlocked flag. This would not be fatal, as the page would be eventually encountered again, but NR_MLOCK accounting would become distorted nevertheless. This patch adds a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that effect. The call site try_to_unmap_cluster() is fixed so that for page != check_page, trylock_page() is attempted (to avoid possible deadlocks as we already have check_page locked) and mlock_vma_page() is performed only upon success. If the page lock cannot be obtained, the page is left without PG_mlocked, which is again not a problem in the whole unevictable memory design. Signed-off-by: Vlastimil Babka Signed-off-by: Bob Liu Reported-by: Sasha Levin Cc: Wanpeng Li Cc: Michel Lespinasse Cc: KOSAKI Motohiro Acked-by: Rik van Riel Cc: David Rientjes Cc: Mel Gorman Cc: Hugh Dickins Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/mlock.c | 2 ++ mm/rmap.c | 14 ++++++++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) --- a/mm/mlock.c +++ b/mm/mlock.c @@ -79,6 +79,7 @@ void clear_page_mlock(struct page *page) */ void mlock_vma_page(struct page *page) { + /* Serialize with page migration */ BUG_ON(!PageLocked(page)); if (!TestSetPageMlocked(page)) { @@ -174,6 +175,7 @@ unsigned int munlock_vma_page(struct pag unsigned int nr_pages; struct zone *zone = page_zone(page); + /* For try_to_munlock() and to serialize with page migration */ BUG_ON(!PageLocked(page)); /* --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1322,9 +1322,19 @@ static int try_to_unmap_cluster(unsigned BUG_ON(!page || PageAnon(page)); if (locked_vma) { - mlock_vma_page(page); /* no-op if already mlocked */ - if (page == check_page) + if (page == check_page) { + /* we know we have check_page locked */ + mlock_vma_page(page); ret = SWAP_MLOCK; + } else if (trylock_page(page)) { + /* + * If we can lock the page, perform mlock. + * Otherwise leave the page alone, it will be + * eventually encountered again later. + */ + mlock_vma_page(page); + unlock_page(page); + } continue; /* don't unmap */ }